Preliminary work in this laboratory has demonstrated that extremely low magnitude (<30 Microstrain) mechanical signals can be osteogenic if applied at a high frequency (5 to 50 Hz). Such high frequency low magnitude strains comprise an important constituent of a bone's strain history, suggesting that these mechanical events could represent a significant determinant of bone morphology. We hypothesize that small increases in high frequency loading, introduced non-invasively into the skeleton via vibration, will stimulate an increase in bone mass without sacrificing bone quality. Considering these strain levels are well below (<1/100th) those which may cause damage to the tissue, we believe these signals hold great potential as a mechanical prophylaxis for osteopenia. Using skeletally mature sheep, a randomized, partial 5x4x3 factorial experimental design, evaluating frequency (7.5, 15, 30, 60 or 120 Hz), duration (5, 10, 20 or 40 min), and intensity (0.1, 0.2 or 0.4g) will be used to determine the efficacy of a non-invasive mechanical device to augment the trabeculae of the tibia and femur. A series of in vivo and ex vivo protocols will be used to quantify the ability of this twelve month mechanical intervention to affect both bone mass and morphology. Dual energy x-ray absorptiometry will determine changes in density as a function of time, dynamic and static histomorphometry will quantify the site-specificity, quality, and extent of the response, and mechanical testing will be used to determine if this treatment influences strength and stiffness of the treated regions of the skeleton. Finally, the most osteogenic mechanical signals will be used to determine if bone density, strength, and stiffness can be recovered in the osteopenic skeleton. These experiments may yield new insights into the mechanisms by which mechanical factors control bone morphology, as well as lead to a novel treatment for osteoporosis.